The disclosure concerns a method to operate a digital printer for double-sided printing of a recording medium with toner particles that are applied with the aid of a liquid developer, in particular a high-speed printer to print to web-shaped or sheet-shaped recording media.
In such digital printers, a latent charge image of a charge image carrier is inked by means of electrophoresis with the aid of a liquid developer. The toner image that is created in such a manner is transferred indirectly (via a transfer element) or directly to the recording medium. The liquid developer has toner particles and cleaning fluid in a desired ratio. Mineral oil is advantageously used as a cleaning fluid. In order to provide the toner particles with an electrostatic charge, charge control substances are added to the liquid developer. Further additives are additionally added, for example, in order to achieve the desired viscosity or a desired drying behavior of the liquid developer.
Such digital printers have been known for a long time, for example from DE 10 2010 015 985 A1, DE 10 2008 048 256 A1, US 2011/0249990 A1, US 005 424 813 A or DE 10 2009 060 334 A1.
A method for operating with liquid developer is known from US 2002/0106220 A1, in which a first toner image is fixed directly on the recording medium upon application. A separate fixing process is required for each page of the recording medium that is to be printed. Moreover, this fixing negatively affects the quality of the surface of the second side of the recording medium as a result of the drying, shrinking, fold formation etc. The print image on the second side is therefore negatively affected in terms of quality.
A method with which a recording medium is printed on both sides by two opposite print groups is known from the document DE 10 2005 023 462 A1. The polarity of the charge of the toner particles in one of the two print groups is hereby changed before the application of the toner particles on the recording medium, whereby a negative effect on the quality of the print image can be created.